Electric Power Steering (EPS) systems use an electric motor that can be coupled directly to either the steering gear or steering column to reduce a driver's effort in steering the vehicle. During operation of the vehicle, the driver will apply a force to the steering wheel in an effort to steer the vehicle. This results in a “driver torque” being applied to a shaft that is coupled to the steering wheel. Torque sensors detect torque being applied to the steering column by the driver, and communicate this information to an electronic control unit. The electronic control unit generates a motor control signal that is applied to the electric motor causing it to generate a “motor assist torque” that is combined with the driver torque. This combined torque is then used to steer the vehicle. This allows varying amounts of assistance to be applied depending on driving conditions.
There are numerous types of unwanted vibrations, noises, pulsations, disturbances, and other forms of fluctuating vibratory energy that can exist in a vehicle; these phenomena are hereafter collectively and broadly referred to as “vibrations.” Vibrations can have many sources, including external sources such as irregular road surfaces, as well as internal sources.
Periodic vibrations caused by internal sources can propagate throughout the vehicle and can cause an undesirable shake or movement of certain vehicle components that is noticeable to the driver. For instance, periodic vibrations generated at the wheel assemblies can combine to create a dynamic torque on a steering wheel column that causes the steering wheel to cyclically turn at small amplitudes in either direction. When this type of event occurs on a flat or smooth road surface, it is all the more apparent to the driver and is sometimes referred to as “smooth road shake” (SRS). SRS generally is most noticeable between approximately 50 to 100 mph, and exhibits a frequency of about 10 to 20 Hz. At 50 mph, smooth road shake occurs at approximately 10 Hz. SRS tends to increase as an approximately linear function of speed, such that, at 100 mph, SRS occurs at approximately 20 Hz. These vibrations can be sensed by the driver of the vehicle and such steering wheel vibrations may be distracting or annoying to the driver.
Accordingly, it is desirable to provide improved methods, systems and apparatus for suppressing steering wheel vibrations in vehicles having an EPS system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.